In a plant manufacturing titanium dioxide-based dyes, 600 kg of sulphur dioxide/trioxide and sulphuric acid (so-called sulphuric fog) were released into the atmosphere over a 45-min stretch. The accident was due to a malfunction of the controller managing atmospheric discharge at the digestion unit where titanium ore was being attacked by H2SO4. The residual gases (SO2, SO3 and H2SO4 cavities) were washed twice (with water and soda) and then removed, at normal pace, through a chimney on the roof. The gas treatment process shutdown caused a pressure surge and opening of a safety valve. The discharge could not be interrupted during the accident sequence since the digestion reaction was exothermic and self-perpetuated beyond a temperature threshold. A passerby sounded the alarm. A malfunction was detected on the alarm network, and the operator was unable to activate the toll-free number assigned for such circumstances. The Industrial Pollution Prevention Office was kept apprised of the situation.

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